1. Field of the Invention
The present invention relates generally to a control system for unmanned vehicles and more specifically to a system which is particularly suited for use in production plants and which enables mass production and/or the like type of assembly work to be carried out using a plurality of such vehicles.
2. Description of the Prior Art
Conventional automotive production lines and the like are arranged basically in the form of a conveyor belt type system which carries work pieces from station to station. At each station various operations such as machining, welding, assembly and the like are performed. However, with such an arrangement a large tooling investment and amount of set up time and work is required and each time the production of a different work piece is required it is necessary to revise the line. This of course usually requires at least one portion of the line be totally dismantled and rebuilt in order to meet the requirements of the new product.
When a production line which is set up for one type of automotive vehicle is changed to a different type, it is inherent that large scale revision of the assembly line must be made before production of the new vehicle can begin. For example, when a line which is set up for the production of a small sub-compact type vehicle is changed to one for a larger type having a larger engine (merely by way of example), it is necessary to at least change the section of the line wherein the chassis is formed, assembled, welded etc. Further, it is inevitable that the number and size of components and parts which must be fed from prepared stocks into the line will change.
In recent times a large number or robots are used on assembly lines to perform welding and the like tasks. In the event of a model change such as mentioned above or the like occurs, a large number of the robots must be reprogrammed (retaught) in order to perform in the desired manner.
In an effort to alleviate some the above programs it has been proposed in JP-A No. 58-192111 to provide autonomous vehicles which can carry components, parts and the like through a factory or like work place. This system has, as shown in FIGS. 1 and 2, included the provision of guide lines 1 and control markers 2 on the road or floor surface 3 on which the vehicle are arranged to run. The vehicles are provided with two groups of sensors 5 and 6, one which senses the guide line and the other which senses the position of the control markers.
The system used in the above mentioned vehicles is arranged in the manner illustrated in FIG. 3. As will be appreciated from this drawing, the outputs of a plurality of mark detection sensors 6 (four shown by way of example) are fed to a sensor switching section 7. This section 7 is selectively controlled by a signal which is outputted by a control circuit 10 hereinafter referred to as a running control circuit) in a manner to determine which of the mark detection sensor outputs in fed to a position determination section 12. This section, as shown, is also supplied positional or map data from a memory 14. In accordance with this data input, a signal is generated and supplied to a running status determination section 16. This section 16 also receives an input from a movement pattern status section 18 and is arranged to output a control signal to the running control circuit or section 10. In response to this input the running control circuit 10 outputs two sensor switching data signals, one (as previously mentioned) to the sensor switching section 7 associated with the mark detection sensors 6 and a second one to a second sensor switching section 20 associated with a plurality (in this case 4) guide line sensors 5. This circuit 10 also outputs a target speed data signal to a servo control section 22.
The latter mentioned section 22 receives a further data input in the form of a guidance error signal from the second sensor switching section 20 via an A/D converter 24. In response to the target speed and guidance error signals the servo control section 22 outputs speed control signals to the left and right wheel motor servo drivers 26, 28.
This system while proving somewhat effective has suffered from the drawback that at least guide lines 1 and markers 2 have to be painted or otherwise provided on the floor of the factory or the like in which the above mentioned autonomous vehicles are arranged to operate. Accordingly, when it is desired to change from one production line layout to another, it is necessary to repaint the floor in a manner which covers over the old lines and establishes new ones appropriate for the new operations. This of course in the case of an automotive production line, means considerable work which must be precisely carried out in order to ensure accurate movement of the vehicles. Alternatively, it is possible to provide a number of patterns on the floor and operate the vehicles in manner to follow one of the patterns. However, this invites erroneous operations. Viz., in the case the lines or patterns become soiled or otherwise deteriorate in brightness and colour, it is likely that the autonomous vehicles will switch from following the intended pattern and follow one that is not in current use.
In the event of an erroneous sensor switching signal or sensor failure, for example, it is highly possible that the vehicle will turn left instead of right, stop when it should not, or worse still, continue when it should stop, and the like. If the batteries which power the device become low in power the vehicle is apt to stop in mid coure and block up the lanes defined by the painted lines and markers.
Moreover, the number of different patterns that can be effectively painted is limited (by effective colours widths and the like) and requires a complex arrangement of markers in order to assure the correct maneuvering of the vehicles.
Another arrangement proposed in order to permit control and movement of autonomous vehicles is disclosed in JM-A No. 61-11772. This arrangement has made use of a ultrasonic radar arrangement which is used to detect the position of a given item and provides circuits which are buried in the floor and which can be selective energized in manner which enables an autonomous vehicle to follow the electromagnetic flux which is produced.
This system however, suffers from the drawbacks of requiring the accurate (and expensive) disposition of the electric lines in the floor and the use of expensive radar units. Further, when used in a factory near welding equipment for example, the influence of noise proves to be a notable problem and can cause the vehicles to be erroneously guided away from the intended path. Accordingly, for this an other reasons, the system cannot be relied upon to provide the required stopping and starting of vehicles as is inherently required.